Securely Deleting Encrypted Data on Linux

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Securely Deleting Encrypted Data on Linux

In this scenario you are the Systems Administrator for a healthcare company. Your manager has tasked you with logging into the fileserver running CentOS Linux 7.7 and securely deleting some sensitive patient data, ensuring that it cannot be easily recovered. No other files should be altered.

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Lab Info

Level

Intermediate

Last updated

Apr 06, 2025

Duration

15m

Challenge

Confirm File Is Readable
Confirm the size and permissions of the file:
```
[cloud_user@$host]$ sudo ls -l /mnt/patient.1
```
Show the contents of the file:
```
[cloud_user@$host]$ sudo cat /mnt/patient.1
```
Challenge

Fill Free Space
Be sure to double check the path, as this command does no error checking and will overwrite data:
```
[cloud_user@$host]$ sudo dd if=/dev/urandom of=/mnt/junk status=progress; sync
```
Challenge

Overwrite File
The shred command is the simplest method. Specifying -x ensures that the filesize remains unchanged:
```
[cloud_user@$host]$ sudo shred -x /mnt/patient.1
```
If the shred command is not available, we can use the following dd command:
```
[cloud_user@$host]$ sudo dd if=/dev/urandom of=/mnt/patient.1 bs=45 count=1 iflag=fullblock status=progress
```

Challenge

Confirm File Was Overwritten and Remove

Show file contents:

[cloud_user@$host]$ sudo cat /mnt/patient.1

Remove file:

[cloud_user@$host]$ sudo rm /mnt/patient.1

Challenge

Restore Free Space
Remove junk file:
```
[cloud_user@$host]$ sudo rm /mnt/junk
```

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